Elevator systems have recently been provided with two features which are thought to save considerable passenger time and increase the carrying capacity of a given elevator installation. The first of these is utilizing destination calls, by which the passenger does not simply call an elevator to his floor, but at the same time informs the elevator of the intended destination floor. This allows the dispatcher (typically a suitably programmed computer) to allocate the call to the most appropriate car, taking into account not only the origin, but also the destination of the passenger.
A second feature causes passengers to enter their calls while still at some distance (equivalent to about ten seconds, in one case) from the elevator, whereby the dispatcher can attempt to cause the elevator to arrive at nearly the same time that the passenger reaches the elevator. The advance calls are entered either automatically by, or in response to pressing keys on, personal radio transmitters which transmit an identification (ID) number utilized to automatically enter a prearranged destination call or a key-selected call.
Typical problems with these systems include calls caused by the person desiring to go to a destination other than his passively-entered, prearranged destination, or deciding not to enter the elevator yet (such as to purchase a newspaper on the way in), or simply changing his mind. Another problem is establishing a correct level of transmission power. If a remote call device transmits with too much power, the call may be entered on the floor above or the floor below the floor on which the passenger carrying the device is located. On the other hand, if the power is too low, calls may not be registered in a desired remote location, thereby upsetting the call allocation scheme of such a system. If multiple receivers are used, then the system must be able to distinguish between independent requests, and an identical request received by more than one receiver. Furthermore, especially during busy periods on a busy floor, many remote devices may be transmitting at once. Although such devices may use conventional spread spectrum transmission or conventional randomly timed transmission to assure that each message will be distinctly recorded, separately from the others, mixup in transmitted messages as between requests for service, notification of call allocation, and the like should be mitigated to reduce the number of false calls.